PRB Articles


Practical Residential Paving

One of the most intriguing aspects of residential-landscape architectural design is the infinite variety of tastes and tasks we encounter.

Most clients show us pictures of what types of looks they like, but don’t know if the looks are applicable in their circumstances. It is our job to consider their “wants” in order to best show them how those can be incorporated into a logical, environmentally friendly and aesthetically pleasing solution.

Many homeowners today are fixing up their current house rather than buying a new one. When dealing with renovations, the first step is to analyze what currently exists, its exact location, condition and description.

Utilizing an engineered survey of the property, begin by preparing an “as-built” plan, showing the current location and description of all existing improvements. Then create an analysis of existing conditions that consider how those elements fit into the owner’s new program.

Follow this with a conceptual/schematic plan, illustrating graphically what could be.

The design begins with how each portion of the property needs to function. Pedestrian and vehicular circulation systems are a starting point as they have specific spatial requirements. Define access into and out of the property, and a means to get around the site.

Functional areas must fulfill requirements pertaining to space allotments for different activities and proximity to compatible uses:

• How many cars are to be accommodated?

• How large is the family?

• How old are the children?

• Does the family entertain frequently?

• Does the family spend a lot of time outside?

• What type of activities are preferred--tennis, basketball, swimming, golf?

The “hardscaping” is typically limited to 60 percent of the property, with a minimum of 40 percent dedicated to pervious open space.

Once the spatial allocations have been met, it is now time to consider the aesthetic and functional considerations:

• What is the preferred architectural style?

• What is the color scheme?

• What types of products best fulfill their intended use?

• Is there a “family” of products that could serve all purposes?

• How much of the budget has been allocated for these items?

• What are the soil and drainage conditions?

Another important design consideration is the environmental friendliness of the proposed finishes. With the continued emphasis on water conservation, sustainability and “xeriscaping,” more of the landscape area that used to be relegated to lawn now needs to be converted to something that either does not use water, or captures and reuses it.

There is also a new emphasis on containing personal drainage versus dumping it into the public drainage system.

When it comes to permeable paving, there are numerous choices available. Whether gravel, crushed recyclable material (such as colored glass) or mulch, these all allow water to percolate through them but need to be contained, or they move. New sub-surface stabilizing products--such as interlocking PVC circles--make these friable materials stable enough to drive over or use a wheelchair on.

Mulch walks can be created from composting existing leaves, clippings, etc. Pine straw is excellent when utilized on slopes, and stays in place better than fine mulch. These products provide a natural look, reduce weed growth, and filter into the soil, improving its composition and water-retaining properties.

Consider the following categories:

Pervious Concrete

This product uses mostly gravel and a binding agent to hold it together. It is stable enough to drive on, and allows percolation through it. It can be colored by choice of aggregate, but typically it’s more utilitarian than aesthetically striking. It can be combined with microbial agents to clean the automobile-produced pollutants from the water, which can then be collected and reused.

Permeable Pavers

Like the concrete product above, these can be made to be completely pervious. They come in many shapes and colors. Another paver type is ribbed to create larger spaces between each paver, so water drains in the joints. These also are available in a number of colors and shapes.

Note: All pervious products require a different base composition than non-pervious ones.

The use of permeable paving depends on the existing soil quality and grade. If the ground is high and stable, then it is a viable alternative. To collect the water and reuse it for irrigation typically requires 2 feet in depth for storage.

Natural Stone

This category is almost limitless, as pavers are available in almost any shape and/or color. When considering stone for a vehicular application, the compressive strength of the material becomes important, as softer materials like sandstone will crack. Nothing less than 4,000 pounds per square inch (psi) should be used.

Interlocking concrete pavers are designed to withstand 8,000 psi. Travertine is a more formal choice, and is available in a number of tones ranging from almost pure white to gold to dark brown or chocolate. It can be cut into any size and recommended for vehicular use, at least 2-1/2 to 3 inches thick when set on a compacted sand base. It can be 1 to 1-1/2-inches thick when set on a concrete slab.

Pedestrian uses can be ¾ of an inch when set on a slab. No pavers larger than 12 x 12 inches are recommended for driveways as they are more prone to cracking. However, one frequently sees 2- x 2-foot or even 3- x 3-foot squares, separated by 3- to 4-inch wide strips or artificial or natural grass. The 6- x 12-inch brick shape makes an excellent border, or can be attractive in a 45-degree herringbone pattern.

Porphry granite is another popular alternative, as it is extremely hard and comes in colors ranging from red to tan to charcoal or black. It has been used for centuries as cobblestone for streets (3-1/2 to 4 inches x 3-1/2 to 4 inches x 3-1/2 to 4 inches thick), and as a random-shape flagstone for walkways.

Clay Brick Pavers

Often a popular choice, clay bricks have excellent compressive strength (approximately 14,000 psi), and have been around for centuries. Colors are typically in the red/tan/charcoal range, and are mostly made in the classic 4- x 8-inch brick shape. Recycling old bricks from metropolitan areas like “old Chicago” gives that antiquated, tumbled look; these have long been used in “Mediterranean”-style architectural projects.

Precast Concrete Pavers

Available in an almost unlimited range of colors and shapes, these have a compressive strength of more than 8,000 psi when used in the 2-3/8- to 3-1/8-inch thickness. Design is limited only by the imagination as the pavers can be used to create delightful patterns and shapes. Three colors can be combined in a single paver, providing a natural variety of colors.

The thicker pavers can be set on a 1-inch-thick bed of concrete screenings, set over a 6-inch compacted road rock base. Note: if using permeable pavers, these setting-bed dimensions change. The location of the project also changes the criteria as colder climates subject to frost-heaving require additional precautions. Consult a professional designer who can provide designs and suggest paving contractors.

Pedestrian Surfaces

One of my favorite mediums is wood decking, as it is easily customized to fit any condition. It is especially useful when accommodating grade changes, and can be built around large existing trees, creating a natural setting.

In the South, old standbys include pressure-treated pine, cypress, cedar, redwood and, more recently, exotic hardwoods from South and Central America.

As there is a new respect for preserving the world’s forests, a number of artificial or “green” decking products have become available. These alternative decking products are made of aluminum, plastics, plastic resins, polypropylenes, bamboo and composite materials combining sawdust and recycled plastic shopping bags. One of the most exciting is made from rice husks and mineral oil. It emulates teak, and is very resistant to absorbing stains.

Avoid plastic lumber made from PVC--not healthy or sustainable.

Making A Decision

There are several factors to consider when making a decking selection:

• Cost. Pressure-treated pine is one of the least expensive natural wood products, and is planted in sufficient quantities to be considered sustainable. Elevated above the ground, it has a 7- to 10-year life in hot and humid conditions, such as South Florida. Hardwoods, such as Ipe, Green-heart, Palupe and teak, are at the upper end of the cost spectrum. Many of the alternative wood products are equally expensive.

• Maintenance. One of the reasons these alternatives are more expensive than natural wood is their “ultra low-maintenance” claim. Softer woods deteriorate faster, expand and contract with the weather, stain more easily, and are susceptible to insect infestation and mildew, where many of these alternatives do not. They also need to be periodically refinished.

• Ease of installation and repair. All of these decking alternatives are better when installed above the existing ground level. Depending on their intended use and weight loads, there are a number of ways to properly support these decks.

Always consult a professional designer, contractor or engineer. Codes vary in different locales.

Typically, another type of wood is used for these below-deck supports, since they come into contact more with moisture. Many of the decking alternatives are grooved on the sides to allow “hidden fasteners” to be used. These have wings that hold one piece of deck to the next, and attach to the support member below. They are much more attractive than screws and nails, which pop up eventually and deteriorate; they create a minimum 1/16- to 1/8-inch space between adjacent planks, allowing water to pass through, so the water must be drained away. However, when a plank needs repairing, these hidden fasteners require disassembling a part of the deck.

When in doubt, consult with a professional, and spend sufficient time becoming educated about the wisest choice for the intended use. Be conscious of the effect choices will have on the environment, and be good stewards of the planet. Good design is sustainable, long-lasting and functional!

Bruce Howard is the President of Bruce Howard & Associates, a landscape-architecture, site-planning and golf-course design firm in Miami, Fla. He can be reached via e-mail at bruce@brucehoward.net.

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